Broaching question
Broaching question
(OP)
We are working on developing a part that has a hex shaped cavity in the center. The hex covers the entire length of the part. The size of the hex will be 0.9825"±.002" across the flats, and the part is rougly 1.5" long.
This issue is the hardness. It's sintered P/M stainless steel. Our part will have a macro hardness in the mid-30s (Rockwell C) but will have a particle hardness in the mid-50's. So we'd essentially be looking at "hard broaching". The part has essentially no elongation properties and a high UTS.
With the high cost of broaching bars, we're a little leery of trying to use our horizontal broaching machine. We've got an inquiry in on rotary broaching, but this looks like we're pushing the limits (based on what I've read).
We are looking at other methods, but I'm curious as to what your opinions might be on the broaching option.
Thanks!
This issue is the hardness. It's sintered P/M stainless steel. Our part will have a macro hardness in the mid-30s (Rockwell C) but will have a particle hardness in the mid-50's. So we'd essentially be looking at "hard broaching". The part has essentially no elongation properties and a high UTS.
With the high cost of broaching bars, we're a little leery of trying to use our horizontal broaching machine. We've got an inquiry in on rotary broaching, but this looks like we're pushing the limits (based on what I've read).
We are looking at other methods, but I'm curious as to what your opinions might be on the broaching option.
Thanks!





RE: Broaching question
Mike Halloran
Pembroke Pines, FL, USA
RE: Broaching question
There are options to coin/size the ID using a coining press, but they require a slightly different and more expensive processing cycle. I'm just trying to evaluate some alternatives.
RE: Broaching question
RE: Broaching question
I've seen splines completed in a preformed hole. I don't recall the amount of metal that was removed.
RE: Broaching question
And the whole hex has to be qualified and within the profile spec. So we're broaching every surface. =(
Rotary broaching was ruled out by the vendor due to the part length, and the broaching bar company I've used in the past for my horizontal machine has used the phrase, "Whoaaaa...hmmmm, that could be fun." I get the feeling I need to pursue another path. =)
Seriously though, if anybody has done something similar, I'd love to hear about it.
RE: Broaching question
It would have to be pretty long to carry any reasonable chip load, given the tiny 'gullets', but I think you could do it with a cable-pulled tool.
Mike Halloran
Pembroke Pines, FL, USA
RE: Broaching question
Here are two examples where the apex of the angle in a hex has been taken out of play while driving. If your application is using the hex for driving it may be possible to adapt something similar to these for your application. both of these forms take some of the precision out of the hex cavity. If you application is antirotation you could also use this approach to take the precision out of the hex.
Note that the Ozat tools have their profile electroformed. Their quanities are large, but the question remains how many machines do they have in production.
http://www.ozat-tools.com/
h
I have several sets of 3 Ozat sockets of the same size from different lots and comparing the inside dimensions with a caliper I can detect no difference in each sets' dimensions.
Do you need the full length of the hex hole?
RE: Broaching question
The diamond hex broach sounds like a good idea, but I don't want to guess what that would cost. The horizontal 4' T15 bar was around $3700...and no clue if I'd get 10 parts or a 1000 off of it.
I've talked to several production broach shops, one broach manufacturer, and a rotary broaching supplier. Nobody wants to touch it, unless on an R&D no-guarantee basis.
I'm still waiting to hear from the high speed broach company outside of Chicago. If that's out, I think we're going to close up the broaching avenue and look into coining (squishing it to size). We'll have added steps to harden it up, but c'est la vie at this point.
Thanks for the ideas guys! This is one of those cases where the customer's "general" quote drawing and finish spec print are deviating a bit. =)
RE: Broaching question
Mike Halloran
Pembroke Pines, FL, USA
RE: Broaching question
That's kind of what we do when we "coin" features. With a high temp PM part, there is still some porosity. So we actually will compress the part in a coining press using a die, core rod, and punches (carbide insert die, carbide core, tool steel punches). The part smooshes inwards and outwards under compression until it is limited by the die wall and core rod surfaces. Then it's ejected from the die and off of the core. You usually see a little more densification towards the surface of the part. We pretty much can qualify the dimensions that way and get a little better surface hardness. The tolerance is a wee bit tight for this part, but the method is pretty similar in principle to what you're suggesting.
It's a neat process to work with, but can be hell sometimes when trying to anticipate which way the material will move.
RE: Broaching question
http://holdenventures.com/BD.aspx
We do a lot small hole burnishing/broaching and have found out that the lubricant is key to tool life and finish. We get very good results with a Ballizing lubricant from Ball-O-Matic, but the life saver is a flash copper plating for the tougher materials.
I've been told that the PC-10 lubriant is very good for ballizing.
http://www.usalubrications.com/mpc-pc10.html
In talking with our production guy he stated that for production run as you state he would gladly give up $3500 tool to get a better feeling of where he is at.
RE: Broaching question
RE: Broaching question
I have been reading this thread with interest, and your second-to-last reply provided one key detail: hex broach manufactured from T15 costs ~ $3700. I think that using PM T15 will yield a tool life (if uncoated) closer to 10 pieces than 1000 pieces. This application would need something really hard and yet still has some toughness, which PM T15 really does not have. I would be looking at grades like Cartech Micro-Melt® Maxamet® Alloy, Crucible CPM® 15V®, etc., possibly with a TD coating.
RE: Broaching question
RE: Broaching question
Ed Danzer
www.danzcoinc.com
www.dehyds.com